Process for the recovery of metals from sulfide ores through electrolytic dissociation of the sulfides

ABSTRACT

A pollution-free process for the electrolytic dissolution of sulfide ores of the metals of Groups IB, II B, V A, VI A, of the Periodic Table and lead in aqueous acidic media with the formation of metal ions and elemental sulfur followed by recovery of the metal ions from solution in the electrolyte media, the process characterized by certain critical process conditions, these being the use of: 1. AN ALKALI METAL AND/OR ALKALINE EARTH METAL CHLORIDE ELECTROLYTE, 2. A SULFIDE FEED OF AVERAGE PARTICLE SIZE SMALLER THAN 60 MESH U.S. Standard, 3. A PH range of about 0.01 - 3.9, 4. AN ELECTROLYTE TEMPERATURE RANGE OF ABOUT 60*-105* C., and 5. AN ANODE CURRENT DENSITY ABOVE ABOUT 12 AMPERES/FT2.

United States Patent Kruesi [4 1 June 27, 1972 [54] PROCESS FOR THE RECOVERY OF 720,235 2/1903 Frasch ..204/107 METALS FROM SULFIDE ORES THROUGH ELECTROLYTIC ZZZ-2231 23752557 311113258 DISSOCIATION OF THE SULFIDES Anomey shcridah, Ross & Burton [72] Inventor: Paul R. Kruesi, Golden, Colo.

[57] ABSTRACT [73] Assignee: Cyprus Metallurgical Processes Corpora- "on, Los Angela Calm A pollution-free process for the electrolytic dissolution of sulfide ores of the metals of Groups lB, ll B, V A, VI A, of the 1 Flledl 1971 Periodic Table and lead in aqueous acidic media with the formation of metal ions and elemental sulfur followed by Appl' recovery of the metal ions from solution in the electrolyte media, the process characterized by certain critical process [52] [1.8. CI. ..204/105 R, 204/107, 204/ l l 1, conditions, these being the use of:

204/117, 204/118, 204/128 51 rm. 0 ..C22d 1/00, C22d m2, C22d 1 /l6 fl and/m metal [58] Field ofSearch ..204/105, 106, 107, 128,109, y

204/1 11, l 14, 115, 117, 118 2. a sulfide feed of average particle size smaller than 60 mesh US. Standard, [56] References Cited 3. a pH range of about 0.01 3.9,

UNITED STATES PATENTS 4. an electrolyte temperature range of about 60-105 C., and 3,616,331 10/1971 O'Neill et a1 ..204/128 an anode current d i above about 12 amperes/ft 2 1,115,351 10/1914 Wagner ....204/107 1,066,855 7/1913 Slater ..204/ 107 20 Claims, No Drawings PROCESS FOR THE RECOVERY OF METALS FROM SULFIDE ORES THROUGH ELECTROLYTIC DISSOCIATION OF THE SULFIDES BACKGROUND OF THE INVENTION There are disclosures in the prior art of processes for the electrolytic recovery of certain metals from their sulfide ores under various conditions. These processes cannot be used for the economic recovery of metals of Groups I B, II B, V A, VI A of the Periodic Table and lead from their sulfide and mixed sulfide ores, particularly low grade ores, for various reasons.

U.S. Pat. No. 2,331,395 discloses the electrolytic recovery from sulfides of certain metals utilizing an alkaline electrolyte, and U.S. Bureau of Mines Technical Progress Report 26, June 1970, entitled Electrolytic Recovery of Metals teaches the recovery by electrolysis of mercury from cinnabar in an alkaline electrolyte. With the exception of antimony, experimentation has shown that the metals of Groups I B, II B, V A, VI A of the Periodic Table and lead cannot be economically recovered by electrolytic processes in an alkaline media. While antimony can be so economically recovered it is more economic to recover it from acidic media. This is supported by theoretical considerations.

In an alkaline media the limit of efficiency in the electrolytic dissolution of metal ions is the electric current required to oxidize the sulfur present from sulfide ion (-2) to sulfate ion (+6). The electric current required to ionize a given quantity of the desired element is readily calculated. As an example, in an alkaline media for the electrolytic dissolution of the minerals argentite, galena, chalcocite, sphalerite, covellite and chalcopyrite, the ampere hours/pound of metal ionized varies from 452 for argentite to 3,240 for chalcopyrite. In contrast, in an acid media, in which elemental sulfur is a product, the ampere hours/pound of metal for the same minerals varies from 1 13 for argentite to 957 for chalcopyrite. This invention comprises a combination of interdependent process parameters through which results are obtained which support the above theoretical data.

U.S. Pat. No. 2,839,461 discloses an electrolytic process for the recovery of nickel from nickel sulfide utilizing an acid sulfate-chloride electrolyte and which is dependent upon a highly conductive nickel sulfide anode, the anode current being passed through a nickel matte anode. It has been found that the metals of Groups I B, II B, V A, VI A of the Periodic Table and lead cannot be economically recovered by electrolysis from their sulfides in an electrolyte containing substantial sulfate ions or by a process in which sulfate ions are produced in appreciable amounts. Furthermore, the process of the above patent is not applicable to economic recovery of these metals because their sulfides are relatively poor electrical conductors. The specific resistivity of the common sulfide minerals, galena, sphalerite, argentite, chalcopyrite and chalcocite varies from 2 X ohmcm for galena, the lowest, to 9.0 X 10' ohm-cm for chalcocite while that for millerite, a nickel sulfide, used in the patent is 3 X 10" ohm-cm. In fact, U.S. Pat. No. 2,839,461 teaches the addition of sulfur to chalcocite to 'convert it to covellite which has about 100 times lower resistivity, thus making a product which is amenable to the process. The process of the referenced patent cannot be applied to base metal sulfides because of their high resistivities.

U.S. Pat. No. 2,761,829 discloses the electrolytic recovery of copper from sulfide ores containing iron sulfides in an acid media in which current densities said to be applicable to in situ mining are so low that the process is economically prohibitive when applied to mined and concentrated ore.

U. S. Pat. No. 3,464,904 relating to the electrolytic recovery of copper and zinc from their sulfide ores discloses the use of a hydrochloric acid electrolyte having a concentration of 5-10 percent. In the absence of alkali or alkaline earth metal chlorides this acidity is so high that it precludes economic recovery of these metals as demonstrated by Example 2 which follows.

Prior to the present time there hasbeen little incentive for the development to commercial application of electrolytic processes for the recovery of metals from sulfide ores. Metals are conventionally recovered from their sulfide ores by pyrometallurgical processes in which sulfur contained in the ores or concentrates is oxidized to sulfur dioxide, of which a substantial portion is released to the atmosphere with con sequent damage to the environment and loss of the sulfur values. Recently promulgated pollution standards have made the pyrometallurgical processes, as presently applied, prohibitive, and have created demands for pollution-free processes. An electrolytic process, requiring only economic quantities of power, in which substantially all of the sulfur in the above metal sulfides related to this invention is converted to elemental sulfur, is an answer to the pollution problem.

Metals are conventionally recovered from their sulfide ores by pyrometallurgical smelting techniques. The high degree of concentration required for economic pyrometallurgical processing, results in the loss of potentially valuable coproduct values which are not readily recovered. The presence of co-product values in the main metal product often results in economic penalties being assessed against the concentrates. Thus, low grade concentrates which are not amenable to physical separation techniques are often considered valueless or of low value because they cannot be processed economically by conventional pyrometallurgical processes.

STATEMENT OF THE INVENTION The term metal sulfide as contained herein is inclusive of the complex as well as the simple sulfide minerals which contain economically recoverable quantities of the specified metals.

The invention is a pollution-free process for recovery of the metals of Groups I B, II B, V A, VI A of the Periodic Table and lead from their sulfide and mixed sulfide ores in which the sulfide is electrolytically dissociated in an acid aqueous media into elemental sulfur and metal ions which are then recovered from solution in the electrolyte media by conventional pollution-free techniques. The electrolysis process is characterized by certain critical process conditions which render it economically feasible, these being the use of I) an alkali metal and/or alkaline earth metal chloride electrolyte, (2) a sulfide feed particle size smaller than 60 mesh U.S. Standard, (3) a pH range of about 001-39, (4) an electrolyte temperature range of about 60-l05 C, and (5) an anode current density above about 12 ampereslft The economic feasibility of the process is dependent upon the current required to produce a given quantity of metal. It is expressed herein as the ampere hours of current required to release a pound of metal. The power requirement will vary for each metal and economic viability will depend somewhat on the cost per pound at which that metal can be produced by present processes. This statement does not take into con sideration recently promulgated air pollution standards which may completely eliminate or drastically limit the economic competition of present air polluting processes.

The process parameters which have been found to control the current requirements for the process are electrolyte composition, feed particle size, operating pH range, operating temperature, and anode current density. As the examples which follow show, these factors are mutually interacting and dependent as respects their effect on current requirements.

It has been found that the sulfide ores of metals of Groups I B, II B, V A, VI A of the Periodic Table and lead are characterized by certain similar properties related to the electrolytic dissociation to elemental sulfur and metal ions therefrom, not possessed by other metal sulfides, which support group classification. For example, these sulfides all have relatively low conductivities, the metal ions are most favorably produced by electrolysis in aqueous alkali metal and/or alkaline earth metal chloride electrolytes at a pH range from about 0.01 to 3.9 using anode current densities above about 12 amperes/ft at a temperature between about 60-l05 C with the sulfide particle feed size being smaller than about 60 mesh US. Standard. The examples which follow illustrate that the power requirements for the process applied to recover the stated metals from their sulfides are well within the limits of commercial feasibility.

The metals which can be recovered from their sulfide and mixed sulfide ores by the process of the invention are those of Groups I B, 11 B, V A, V] A of the Periodic Table and lead. Although antimony, bismuth, cadmium and selenium were recovered in Example 7 which follows as trace metals, the process is operative for recovering them regardless of the amounts existing in the ores or minerals. The minerals to which the process is applicable often contain the metals in the form of complex or mixed sulfides.

The electrolyte media for the process must be acidic as an alkaline electrolyte has proven unsatisfactory for recovery of the defined metals to which the invention is related. Elemental sulfur is not stable in'an alkaline media because oxidation of the sulfur proceeds rapidly in this media through thiosulfate, hydrosulfite, sulfite to sulfate. The presence of sulfate ions is undesirable because at high sulfate concentrations oxygen is rapidly evolved at the anode resulting in a decrease in current efficiency. Further, it was found that at high current densities in the presence of sulfate, graphite anodes were appreciably attacked.

The preferred electrolyte media is an aqueous acidic solution of alkali metal chloride or alkaline earth metal chloride, or mixtures thereof. The chlorides of sodium, potassium, barium and calcium, or mixtures thereof have been found suitable. Concentrations within the range of 0.5-4N or saturation may be used. Voltage across the cell is lower at higher salt concentrations so that the latter are preferred except where low grade feeds are used and where salt losses would therefore become significant.

It is highly important that a high percentage of the sulfur in the metal sulfidebe recovered as elemental sulfur both from the standpoint of pollution control and the electrical efficiency of the process. if sulfur is converted to sulfate, the disposal of the latter may create a pollution problem. Every mole of sulfur which is oxidized beyond the elemental state requires 6 Faradays which is equivalent to 2,275 ampere hours per pound of sulfur. As chalcopyrite, for example, contains approximately one pound of sulfur per pound of copper, any sulfur oxidation to the sulfate represents a substantial loss of efficiency. As shown by the examples below, an average of at least 90 percent of the sulfur in the sulfides is converted to elemental sulfur in the process of the invention. The elemental sulfur does not result in any polarization problems at the reaction temperatures of the electrolyte media.

The particle size of the feed material is critical as it directly affects the conversion to elemental sulfur. The elemental sulfur produced is extremely fine. The anode current attacks the metal sulfide preferentially to sulfur, provided the sulfide has sufficient activity near the anode. The activity of the sulfide is a function of its concentration and its exposed surface area. Therefore, the presence of a high concentration of fine sulfide near the anode prevents the continuing oxidation of sulfur and results in higher efficiency and consequently lower current consumption, as explained above. An average grain size range for the feed sulfide smaller than about 60 mesh US. Standard is the operable range and is compatible with other critical parameters.

A pH range for the electrolyte media between about 0.01 and 3.9 is preferred. Current efficiency is reduced at pHs above 3.9, and at very high acidities (low pH values) in the absence of substantial concentrations of alkali or alkaline earth, metal chlorides. The preferred pH range for lead, silver and zinc sulfides is about 2.0 3.0, the most preferred pH being about 2.5. The preferred range for copper sulfides is 0.5 1.5 with about l.0 being most preferred.

The reaction temperature of the electrolyte is critical and high process efiiciency is not obtained at low temperature. In

the case of chalcopyrite, for example, the preferential attack on the sulfide over elemental sulfur is'accentuated at high temperatures. At lower temperatures more sulfate is produced. A temperature range of about 60-l05 C is the operable range when used in conjunction with the other critical factors. A temperature of C is most preferred.

The current density is also critical as used with the other critical parameters with a preferred range being above about 12 ampereslft In contrast to some previous teaching (U.S. Pat. No. 2,761,829) it was found that high copper dissociation in the presence of iron sulfides was attained at current densities up to 600 amperes/ft? For the mixture of chalcopyrite and iron sulfide where chalcopyrite is the predominant mineral, a preferred current density range is about 200-480 amperes/ft with the most preferred value being about 300 amperes/ft. Where iron sulfide predominates current densities between 50-120 amperes/ft are preferred. In the case of the sulfides of lead, silver and zinc, and copper sulfides such as chalcocite and covellite, current densities between about 40-360 amperes/ft are referred. With high grade concentrates a range of 120-360 amperes/ft is most preferred, a range of 50-1 20 ampereslft being most preferred with low grade feeds.

The following examples with results are illustrative of the process of the invention but not limiting thereof. Two types of apparatus, both known in the art, were used in performing the examples. In the first (designated non-diaphragm) an anode of a suitably corrosion resistant material such as graphite is placed opposite a cathode of a suitable material such as stainless steel. An agitator is positioned in a corrosion resistant container in such a manner as to keep the mineral being at tacked in an active suspension in the acidic aqueous salt media, and to force said mineral continuously against the anode. A suitable means of supplying heat supplemental to the heat generated by the electrolysis is provided. This type of apparatus is well known and may of course be modified by supplying a multiplicity of anodes and cathodes.

A second and more efficient device, also known in the art,

and here designated diaphragm cell was used. It consists of two anodes made of graphite or other suitable corrosion resisting material each on one side of a cathode made of stainless steel. The anodes are separated from the cathode by a space and by a cloth (filter cloth of suitable plastic) which then forms a cathode compartment and an anode compartment. Provision is made for circulating the mineral feed and anolyte past the anodes by means of a pump. Similarly, a pump circulates the catholyte past the cathode. Provision is made by means of valves for transferring catholyte to anolyte or (after filtration to remove feed) anolyte to catholyte. Supplemental heating of the circulating anolyte is also provided. Again, this type of cell is well known in the art and may be provided with a multiplicity of anodes and cathodes.

Examples 2, 3, 5-9, 13 and 14 were run using diaphragm type cells, with non-diaphragm type cells being used in the remaining examples.

Grain size is given in US. Standard mesh size, current density is given in amperes/ft", current requirement is reported in terms of ampere hours/pound of metal dissociated, and recovered sulfur is based on grams of elemental sulfur dissociated/gram of non-ferrous metal dissociated.

In Examples l-7, inclusive, the feed material was a commercial chalcopyrite copper concentrate assaying 26.6 percent copper, .l.63 percent zinc, 0.24 percent lead, 0.048 percent antimony, 0.11 percent selenium and by mineral examination consisting of about percent chalcopyrite and 6 percent pyrite and about 4 percent other metals.

EXAMPLE 1 A series of tests were run to demonstrate the effect of the composition of the electrolyte upon the efficiency of dissolving copper from chalcopyrite. In each case a slurry of grams of feed in 1,800 milliliters of electrolyte was made and subjected to 60 ampere hours of current.

Media BaCli KCl N aCl-CaClz KCl-CaClg NaCl-NagSOr Concentrations 4 N 2 N pII 3. 3. 0 Temperature C.) 80 70 Grain size 200 -270 Anode current density. 360 240 Current requirement 2, 320 2, 720

As may be noted, alkali chlorides and alkaline earth metal chlorides are very effective as electrolytes. Sodium chloridesodium sulfate electrolyte as taught in US Pat. No. 2,893,461 proved unsatisfactory and a substantial evolution of oxygen at the anode was noted. The efficiency of this electrolyte was about a factor of four poorer than those tests where sulfate concentration was low.

' EXAMPLE 2 A series of tests were run to demonstrate the effect of acidity (pH) upon the efficiency of dissolving copper from a chalcopyrite concentrate. In each case a slurry of 200 grams of feed in 1,800 milliliters of electrolyte was used and subjected to 30 ampere hours of current.

ACIDITY acidity HCl 5% l-lCl pH 0.5 PH 1.0 pH 3.0

(pH 0.01) (PH 0.01) media no salt 4N NaCl 4N NaCl 4N NaCl 4N NaCl Temp. (C) 80 80 80 80 80 grain size 270 270 270 270 270 anode current density 120 120 120 120 120 current requirement 1560 517 605 590 recovered sulfur 0.85 0.93 0.91 0.98 0.89

The use of 5% H Cl electrolyte is taught in US. Pat. No. 3,464,904. it is noted that the'use of such strong acidity in the absence of a chloride salt in the electrolyte results in low efficiency. For a 5 percent H Cl electrolyte in the absence of sodium chloride the efficiency is reduced about two-thirds and the conversion of the sulfide sulfur to elemental sulfur is substantially reduced. The presence of 4N sodium chloride counteracts this reduced efficiency.

EXAMPLE 3 A series of tests were run to demonstrate the effect of temperature upon the efficiency of dissolving copper from a chalcopyrite concentrate. in each case a slurry of 200 grams of feed in 1,800 milliliters of electrolyte was used and subjected to 30 ampere hours of current.

Temperature (C) 30 80 Media 4N NaCl 4N NaCl pH 3.0 3.0 Grain Size -270 270 Anode Current Density 120 120 Current Requirement 1540 885 Recovered Sulfur 0.7 0.89

Grain Size +90 Media 2N NaCl 2N NaCl 2N NaCl pH 2.3 2.4 3.0 Temperature (C) 70 70 70 Anode current density 240 240 240 Current Requirement 4400 3400 2180 The very substantial improvement with small grain size is apparent.

EXAMPLE 5 A series of tests were run to demonstrate the effect of anode current density upon the efficiency of dissolving copper from chalcopyrite concentrate. In each test a slurry of 200 grams of As will be noted, contrary to the teachings of US. Pat. No. 2,761,829, efficiency is not limited by the use of high current densities.

EXAMPLE 6 Example 6 illustrates the operability of the process at a chloride salt electrolyte concentration as low as 1N Feed was 200 grams of the chalcopyrite concentrate previously used and dispersed in two liters of electrolyte and subjected to 30 ampere hours of current.

Media 1N NaCl pH 0.5 Temperature (C) Grain Size 270 Current Requirement 646 Anode Current Density Recovered Sulfur 0.94

EXAMPLE 7 A test was run to demonstrate that trace metal values can be recovered in the process along'with copper. The feed was two kilograms of the chalcopyrite concentrate. it was dispersed in 27 liters of electrolyte and subjected to 400 ampere hours of current.

Media 3N KCl pH 2.0 Temperature (C) 60C Grain Size -270 Anode Current Density 480 Current Requirement 1720 Cu recovered 22.8 zinc recovered 55.0 lead recovered 71.0 antimony recovered 59.0 selenium recovered 42.0 cadmium recovered l 1.0 bismuth recovered 8.0

4N NaCl Media pH 3.0 Temperature (C) 80 Grain Size 270 Anode Current Density 60 Current Requirement 700 It is noted that an anode current density as high as 60 amperes/ft is entirely satisfactory with only 700 amperes hr/lb Cu required.

EXAMPLE 9 A test using a different cupreous pyrite concentrate containing 2.0 percent copper was run. A feed of 200 grams was slurried with 2,400 milliliters of electrolyte and subjected to ampere hours of current.

Media 4N NaCl pH 3.0 Temperature (C) 80 Grain Size -270 Anode Current Density 54 Current Requirement 947' Examples 8 and 9 conclusively prove that high anode current densities are effective on pyrite containing copper sulfides.

EXAMPLE to To demonstrate the effectiveness of the process on galena, a test was run ona commercial lead concentrate con-taining 63.4 percent lead. A feed of 25 grams was slurried with 1,500 milliliters of electrolyte and subjected to l0 ampere hours of current.

Media 2N KCl pH 2.0 Temperature (C) 70 Grain Size 270 Anode Current Density 120 Current Requirement 366 The residue contained 28.9 percent elemental sulfur or 0.134 grams of sulfur for each gram of lead dissolved which is the stoichiometric amount of sulfur in the mineral galena.

EXAMPLE ll To demonstrate the effectiveness of the process on zinc sulfide a test was run on a commercial zinc concentrate containing 48.7 percent zinc and 3.0 percent lead. A feed of 50 grams was slurried with 1,900 milliliters of electrolyte and subjected to 30 ampere hours ofcurrent.

Media 2N KC] pH 2.0 Temperature (C) 70 Grain Size 270 Anode Current Density 120 Current Requirement 586 The residue contained 43.7 percent elemental sulfur or 0.41 grams per gram of zinc dissolved.

EXAMPLE 12 A test was run on a mixed zinc-lead-silver concentrate. The feed analyzed 35.4% Zn, 22.0% Pb, 0.021% Ag. A feed of 100 grams was slurried in 1,700 milliliters of electrolyte and sub jected to 60 amperes hours of current.

Media 2N KCl 0.04N CaCl pH 2.5

Temperature (C) 70 Grain Size 270 Anode Current Density 240 Current Requirement 517 Zinc recovery 85% Lead Recovery 100% Silver recovery 81% The residue assayed 40.5 percent elemental sulfur or 0.268 grams per gram of zinclead dissolved.

This example demonstrates the effectiveness of the process on mixed lead, zinc and silver ores. The example further illustrates the equivalency of these metals and their sulfides in the process.

EXAMPLE 13 A low grade zinc-copper concentrate containing substantial pyrite impurity was tested. The concentrate assayed 5.9 percent copper, 25.4 percent zinc, and 20.2 percent iron. The copper was chiefly in the form of chalcopyrite. A feed of 200 grams was slurried in 3,800 milliliters of electrolyte and subjected to 30 amperes hours of current.

Media 4N NaCl pH 2.5 Temperature (C) Grain Size 270 Anode Current Density 120 Current Requirement 617 Copper recovered 31.5% Zinc recovered 36.2%

Examples 12 and 13 demonstrate the effectiveness of the process for mixtures of sulfides of the metals on which the process is effective. Along with other examples they show the effectiveness of the process for these metals.

EXAMPLE 14 A feed of 200 grams of a low grade gold ore which assayed 0.5 oz. of gold per ton and 2.7 percent arsenic was slurried with L600 milliliters of electrolyte and subjected to 15 ampere hours of current.

Media 2N NaCl pH above 3 Temperature (C) 70 Grain Size 60 Anode Current Density 60 Power Requirement I020 KW hrs/oz. of gold Gold Recovered 50% Arsenic recovered 32% The results show the process is operative for the recovery of gold or arsenic.

The power requirements set forth in the examples are well within commercial feasibility ranges for large scale production of the metals from their sulfide and mixed sulfide ores. The cost of the recovery of the metals from the electrolyte after electrolysis by conventional techniques is comparatively small. The process permits the recovery in significant yields of metals present in trace quantities. The high percentage recovery of sulfur from the sulfides as elemental sulfur substantially reduces the pollution problems associated with prior art processes. Accordingly, the invention provides a process for recovery of the metals from their sulfide and mixed sulfide ores which has the advantages of being commercially feasible and pollution free.

I claim:

1. A process for the recovery of metals of Groups I B, I] B, V A, VI A of the Periodic Table and lead from their sulfides and mixed sulfides, and mixtures thereof, by electrolysis with the formation of elemental sulfur-and, metal ions, which process comprises:

a. providing an electrolyte in an electrolytic cell including at least an anode and a cathode, the electrolyte comprising an acidic aqueous solution of at least one chloride salt selected from the group consisting of alkali metal chlorides and alkaline earth metalchlorides, the solution having a concentration from about IN to saturation;

b. mixing with the electrolyte a solid feed sulfide of the metal having an average particle size smaller than about 60 mesh 05. Standard;

0. maintaining the temperature of the electrolyte media at about 60 to C, and the pH of the electrolyte media below about 3.9 while introducing electric current into the electrolytic cell to provide an anode current density above about 12 amperes per square foot to recover the elemental sulfur; and

d. recovering the metal from the electrolyte.

2. The process of claim 1 in which the sulfide from which the metal is recovered is characterized by having a specific resistivity of at least 1 'l0"' ohm-cm.

3. The process of claim 1 in which the metal is recovered from the sulfide in the presence of iron sulfides.

4. The process of claim 1' including the final step of recovering the metal from solution in the electrolyte by electrodeposition on the cathode.

5. The process of claim 1 in which the metal recovered is copper.

6. The process of claim 1 in which the metal recovered is lead.

' 7. The process of claim 1 in which the metal recovered is silver.

8. The process of claim 1 in whichthe metal recovered is zinc.

9. The process of claim 1 in which the metal recovered is antimony.

10. The process of claim 1 in which the metal recovered is arsenic.

1 l. The process of claim 1 in which the metal recovered is bismuth.

12. The process of claim 1 in which the metal recovered is cadmium.

13. The process of claim 1 in which the metal recovered is selenium.

14. The process of claim 1 in which the metal recovered is gold.

15. The process of claim 1 in which the alkali metal chlorides are sodium and potassium chlorides and the alkaline earth metal chlorides are calcium and barium chlorides.

16. The process of claim 1 in which the metal is copper and a pH between about 0.5 and 1.5 is used.

17. The process of claim 1 in which the metal is selected from the group consisting of zinc, lead and silver and a pH between about 0.5 and 3.0 is used.

18. The process of claim 1 in which the metals are selected from the group consisting of antimony, arsenic, bismuth, cadmium, copper, gold, lead, selenium, silver and zinc.

19. In the process for the electrolytic recovery of sulfur and metals of Groups I B, ll B, V A, VIA of the Periodic Table and lead from their sulfides and mixed sulfides, the improvement which comprises:

a. conducting the electrolysis in an electrolyte media comprising an acidic aqueous solution of at least one chloride salt selected from the group consisting of alkali metal chlorides and alkaline earth metal chlorides, the solution having a concentration from about IN to saturation;

b. utilizing a feed sulfide of the metal having an average particle size smaller than about 60 mesh US. Standard;

c. maintaining the temperature of the electrolyte media at about 60- C;

d. maintaining the pH of the electrolyte media between about 0.01 3.9;

e. using an anode current density in excess of about 12 amperes per square foot.

20. A process for the dissociation of metals from their sulfides, mixed sulfides, and mixtures thereof, by electrolysis with the formation of elemental sulfur, which process comprises:

a. providing an electrolyte in an electrolytic cell including at least an anode and a cathode, the electrolyte comprising an acidic aqueous solution of at least one chloride salt selected from the group consisting of alkali metal chlorides and alkaline earth metal chlorides, the solution having a concentration from about IN to saturation;

b. mixing with the electrolyte a solid feed sulfide of the metal having an average particle size smaller than about 60 mesh US. Standard; and

c. maintaining the temperature of the electrolyte media at about 60 to 105 C, and the pH of the electrolyte media between about 0.01 to about 3.9 while introducing electric current into the electrolytic cell to provide an anode current density above about 12 amperes per square foot to dissociate the metal sulfide into metal ions and elemental sulfur.

4 CERTIFICATE CORRECTION Patent NO- 3.673.061 Dated June 27. 1972 Inventor(s) Paul R. Kruesi It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the table in Example 1, Column 5, BaCl in the heading should be BaCl In the "acidity" table in Example 2, Column 5, the current requirement in the last column should be 900 In the results of Example 4, Column 5, the grain size in the I first column should be +80 rather than +90.

Signed and sealed this 15th day of May 1973.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents FORM PO-1050 (10-69) USCOMM-DC 60376-P69 u.s. GOVERNMENT PRINTING OFFICE: 1969 o-sss-au. 

1. AN ALKALI METAL AND/OR ALKALINE EARTH METAL CHLORIDE ELECTROLYTE,
 2. A SULFIDE FEED OF AVERAGE PARTICLE SIZE SMALLER THAN 60 MESH U.S. STANDARD,
 2. The process of claim 1 in which the sulfide from which the metal is recovered is characterized by having a specific resistivity of at least 1 X 10 5 ohm-cm.
 3. The process of claim 1 in which the metal is recovered from the sulfide in the presence of iron sulfides.
 3. A PH RANGE OF ABOUT 0.01-3.9,
 4. AN ELECTROLYTE TEMPERATURE RANGE OF ABOUT 60*-105*C., AND
 4. The process of claim 1 including the final step of recovering the metal from solution in the electrolyte by electrodeposition on the cathode.
 5. The process of claim 1 in which the metal recovered is copper.
 5. AN ANODE CURRENT DENSITY ABOVE ABOUT 12 AMPERES/FT2.
 6. The process of claim 1 in which the metal recovered is lead.
 7. The process of claim 1 in which the metal recovered is silver.
 8. The process of claim 1 in which the metal recovered is zinc.
 9. The process of claim 1 in which the metal recovered is antimony.
 10. The process of claim 1 in which the metal recovered is arsenic.
 11. The process of claim 1 in which the metal recovered is bismuth.
 12. The process of claim 1 in which the metal recovered is cadmium.
 13. The process of claim 1 in which the metal recovered is selenium.
 14. The process of claim 1 in which the metal recovered is gold.
 15. The process of claim 1 in which the alkali metal chlorides are sodium and potassium chlorides and the alkaline earth metal chlorides are calcium and barium chlorides.
 16. The process of claim 1 in which the metal is copper and a pH between about 0.5 and 1.5 is used.
 17. The process of claim 1 in which the metal is selected from the group consisting of zinc, lead and silver and a pH between about 0.5 and 3.0 is used.
 18. The process of claim 1 in which the metals are selected from the group consisting of antimony, arsenic, bismuth, cadmium, copper, gold, lead, selenium, silver and zinc.
 19. In the process for the electrolytic recovery of sulfur and metals of Groups I B, II B, V A, VI A of the Periodic Table and lead from their sulfides and mixed sulfides, the improvement which comprises: a. conducting the electrolysis in an electrolyte media comprising an acidic aqueous solution of at least one chloride salt selected from the group consisting of alkali metal chlorides and alkaline earth metal chlorides, the solution having a concentration from about 1N to saturation; b. utilizing a feed sulfide of the metal having an average particle size smaller than about 60 mesh U.S. Standard; c. maintaining the temperature of the electrolyte media at about 60*- 105*C; d. maintaining the pH of the electrolyte media bEtween about 0.01 - 3.9; e. using an anode current density in excess of about 12 amperes per square foot.
 20. A process for the dissociation of metals from their sulfides, mixed sulfides, and mixtures thereof, by electrolysis with the formation of elemental sulfur, which process comprises: a. providing an electrolyte in an electrolytic cell including at least an anode and a cathode, the electrolyte comprising an acidic aqueous solution of at least one chloride salt selected from the group consisting of alkali metal chlorides and alkaline earth metal chlorides, the solution having a concentration from about 1N to saturation; b. mixing with the electrolyte a solid feed sulfide of the metal having an average particle size smaller than about 60 mesh U.S. Standard; and c. maintaining the temperature of the electrolyte media at about 60* to 105* C, and the pH of the electrolyte media between about 0.01 to about 3.9 while introducing electric current into the electrolytic cell to provide an anode current density above about 12 amperes per square foot to dissociate the metal sulfide into metal ions and elemental sulfur. 